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Yasuyuki Kimura

Publications and source records attributed to Yasuyuki Kimura.

13 recordsLinked to original sources
PubMed2006

Study of internal structure of meso-tetrakis (4-sulfonatophenyl) porphine J-aggregates in solution by fluorescence microscope imaging in a magnetic field.

To determine the internal molecular arrangement of organic dye aggregates, a technique for observing the fluorescence microscope image of a solution consisting of dye aggregates in a magnetic field was developed. Using this technique, the fluorescence image of meso-tetrakis (4-sulfonatophenyl) porphine (TPPS) J-aggregates in a solution in a magnetic field of 10 T was observed. It was observed that individual rod-shaped TPPS aggregates (4-20 microm in length) were aligned parallel to the applied field. The polarized absorption spectra of the sample solution were also measured in the fields of up to 10 T. The spectra show the magnetic field dependence of the J-band intensity, reflecting the magnetic alignment of the aggregates. On the basis of the magnetic and optical properties obtained by the experiments, it was proposed that TPPS J-aggregates have a tube-like structure and are constructed from one-dimensional molecular arrays that are stacked parallel to the long axis of the tube.

Journal Article↗
PubMed2006

Effect of linearization correction on statistical parametric mapping (SPM): a 99mTc-HMPAO brain perfusion SPECT study in mild Alzheimer's disease.

OBJECTIVE: Statistical parametric mapping (SPM) was employed to investigate the regional decline in cerebral blood flow (rCBF) as measured by 99mTc-hexamethyl propylene amine oxime (HMPAO) single photon emission computed tomography (SPECT) in mild Alzheimer's disease (AD). However, the role of the post reconstruction image processing on the interpretation of SPM, which detects rCBF pattern, has not been precisely studied. We performed 99mTc-HMPAO SPECT in mild AD patients and analyzed the effect of linearization correction for washout of the tracer on the detectability of abnormal perfusion. METHODS: Eleven mild AD (NINCDS-ADRDA, male/female, 5/6; mean+/-SD age, 70.6+/-6.2 years; mean+/-SD mini-mental state examination score, 23.9+/-3.41; clinical dementia rating score, 1) and eleven normal control subjects (male/female, 4/7; mean+/-SD age, 66.8+/-8.4 years) were enrolled in this study. 99mTc-HMPAO SPECT was performed with a four-head rotating gamma camera. We employed linearization uncorrected (LU) and linearization corrected (LC) images for the patients and controls. The pattern of hypoperfusion in mild AD on LU and LC images was detected by SPM99 applying the same image standardization and analytical parameters. A statistical inter image-group analysis (LU vs. LC) was also performed. RESULTS: Clear differences were observed between the interpretation of SPM with LU and LC images. Significant hypoperfusion in mild AD was found on the LU images in the left posterior cingulate gyrus, right precuneus, left hippocampus, left uncus, and left superior temporal gyrus (cluster level, corrected p < 0.005). With the LC images, significant hypoperfusion in AD was found only in the bilateral posterior cingulate gyrus and left precuneus (cluster level, corrected p < 0.005). A pattern of greater rCBF distribution at the high flow cortices and low flow cortices was observed on LC and LU images, respectively, in the case of both controls and mild AD patients. CONCLUSION: Hippocampal hypoperfusion could be detected by means of SPM in the LU images but not in the LC images. The results of SPM may vary in 99mTc-HMPAO SPECT with or without linearization correction, which should be carefully evaluated when interpreting the pattern of rCBF changes in mild Alzheimer's disease.

Aged↗
PubMed2006

Diastolic blood pressure influences cerebrovascular reactivity measured by means of 123I-iodoamphetamine brain single photon emission computed tomography in medically treated patients with occlusive carotid or middle cerebral artery disease.

OBJECTIVE: Impaired cerebrovascular reactivity (CVR) to vasodilating agents is a predictor of the onset and prognosis of ischemic stroke. It is realized that the CVR improves or worsens when measured periodically during the clinical course in medically treated patients with occlusive cerebrovascular disease. In these patients, we investigated the possible relationship between the interval change in CVR and that in systemic blood pressure (BP). METHODS: Forty-two patients (14 females and 28 males, mean age +/- SD: 65.3 +/- 8.8 years) with severe stenosis or occlusion of the common carotid, internal carotid, or middle cerebral arteries repeatedly underwent single photon emission computed tomography (SPECT) studies using 123I-iodoamphetamine to measure cerebral blood flow (CBF) distribution and CVR at a more-than-6-month interval (mean +/- SD: 18.5 +/- 8.8 months). The CVR was separately estimated in cerebral hemispheres ipsilateral and contralateral to the most severe vascular lesion as the % increase in CBF after acetazolamide loading to CBF at rest. Systemic BP was measured four times at enrollment and the follow-up SPECT studies during resting and acetazolamide loading. Average BP at each SPECT study was an average of BP measurements during resting and acetazolamide loading. Interval changes in CVR were correlated with those in average systolic BP, average diastolic BP, and average mean arterial BP. RESULTS: The interval changes in CVR were significantly correlated with those in average diastolic BP in the ipsilateral hemisphere (y = 0.71x + 1.43, r2 = 0.11, p < 0.05) and in the contralateral hemisphere (y = 0.88x - 0.46, r2 = 0.16, p < 0.05) but not with those in average systolic BP or average mean arterial BP. CONCLUSIONS: In medically treated patients with steno-occlusive carotid artery or middle cerebral artery lesions, the interval change in CVR to acetazolamide by means of 123I-IMP SPECT was influenced by the diastolic BP at the SPECT studies. Monitoring diastolic BP is important to evaluate interval change in CVR.

Acetazolamide↗
PubMed2005

Optical waveguide self-assembled from organic dye molecules in solution.

Fiber-shaped H-aggregates with lengths of up to 300 microm are synthesized by self-assembly of thiacyanine (TC) dye molecules in solution. Photoluminescence (PL) images and spatially resolved PL spectra of the fibers that are transferred onto a glass substrate reveal that the fibers act as single-mode optical waveguides that propagate PL in the range of 520 to 560 nm over 250 microm without any loss.

Carbocyanines↗
PubMed2005

Hemodynamic influences of losartan on the brain in hypertensive patients.

The effects of angiotensin II receptor blockers on cerebral hemodynamics in humans have not been well elucidated. The present study evaluated the effects of losartan on cerebral hemodynamics in hypertensive patients using positron emission tomography. Ten patients with essential hypertension (mean age, 60.8 years) were examined. In each patient, regional cerebral blood flow was measured by [O-15] labeled water positron emission tomography before and after the oral administration of losartan for 8 to 23 weeks. In 8 patients, the baseline regional cerebral blood flow measurement was followed by 1,000 mg of acetazolamide challenge to measure the cerebral perfusion reserve. Systemic blood pressures before and after treatment were 153.8 +/- 10.8/96.0 +/- 6.5 mmHg (systolic mean +/- SD/diastolic mean +/- SD) and 133.4 +/- 11.2/83.6 +/- 6.5 mmHg, respectively; this difference was significant. The baseline global cerebral blood flow values before and after treatment were 38.4 +/- 6.9 ml/min/100 g and 38.2 +/- 8.2 ml/min/100 g, respectively; this difference was not significant. The results of the global cerebral blood flow response to the acetazolamide challenges were not statistically different before and after treatment. A regional analysis showed no statistical difference in regional cerebral blood flow or cerebral perfusion reserve throughout the brain before and after treatment. Losartan's effect on reducing the blood pressure did not affect either the baseline regional cerebral blood flow or the cerebral perfusion reserve in patients with mild to moderate hypertension. The inclusion of losartan in anti-hypertensive regimens could be advantageous for cerebral circulation in patients with essential hypertension.

Aged↗
PubMed2004

Electrophoretic microrheology of a dilute lamellar phase: relaxation mechanisms in frequency-dependent mobility of nanometer-sized particles between soft membranes.

Viscoelastic properties of complex fluids in the microscopic scale can be studied by measuring the transport properties of small, embedded probe particles. We have measured the complex electrophoretic mobility micro*(omega) of nanometer-sized particles dispersed in a lyotropic lamellar phase, which shows two relaxation processes at approximately 1 kHz (high frequency relaxation, HF) and 1 Hz (low frequency relaxation, LF). It is shown quantitatively that these processes are caused by the trapping of particles within two local structures of characteristic size in the lamellar phase: the interbilayer distance and the persistence length. The origin of observed relaxations is further investigated and augmented in this study with data obtained by two other complementary methods, dielectric spectroscopy and the direct observation of fluorescently labelled probe particles under an optical microscope. It is shown that the local distortion field of the lamellar phase is induced by the extra steric interaction involving the collision of a colloidal particle with the membrane. The resulting distortion field hinders the Brownian motion of colloidal particles parallel to the membranes (not vertical), and causes the observed HF relaxation. On the other hand, the origin of LF relaxation is presumably a result of the defects in the lamellar structure. Since the results of this study show that the transport property is strongly influenced by microscopic environments, this method is referred to as electrophoretic microrheology.

Colloids↗
PubMed2004

Spectral analysis of 99mTc-HMPAO for estimating cerebral blood flow: a comparison with H2(15)O PET.

Cerebral blood flow (CBF) can be quantified non-invasively using the brain perfusion index (BPI), which is determined using radionuclide angiographic data obtained through the use of technetium-99m hexamethylpropylene amine oxime (99mTc-HMPAO). The BPI is generally calculated using graphical analysis (GA). In this study, BPI was measured using spectral analysis (SA), and the usefulness of SA was compared with that of GA. Thirteen patients with various brain diseases and four healthy male volunteers were examined using radionuclide angiography with 99mTc-HMPAO. The BPI was measured for each subject using both SA and GA. In the four healthy volunteers, the BPI was examined at rest and after the intravenous administration of 1 g of acetazolamide (ACZ). An H2(15)O PET examination was also performed in the 13 patients; the BPIS and BPIG values were compared with the CBF measurements obtained using H2(15)O PET (CBFPET). The BPI values obtained by SA (BPIS) (x) and by GA (BPIG) (y) were correlated (y = 0.568x + 0.055, r = 0.901) in the 13 patients and four healthy volunteers at rest, although the BPIG values were underestimated by 36.1 +/- 7.5% (mean +/- SD) compared with the BPIS values. The degree of underestimation tended to increase with increasing BPIS values. The increase in the BPIS was 32.1 +/- 8.0% after the intravenous administration of ACZ, while the increase in BPIG was only 8.1 +/- 2.8%. This discrepancy was considered to be the result of the BPIG values being affected by the first-pass extraction fraction of the tracer. Although both BPIS and BPIG values were significantly correlated with the CBFPET values, the correlation coefficient for BPIS was higher than that for BPIG (BPIS: r = 0.881; BPIG: r = 0.832). These results suggest that SA produces a more reliable BPI for quantifying CBF using 99mTc-HMPAO than the conventional method using GA. The SA method should be especially useful for activation studies involving pharmacological intervention and/or clinical cases with an increased CBF.

Adult↗
PubMed2004

Cerebral hemodynamics and metabolism in adult moyamoya disease: comparison of angiographic collateral circulation.

PURPOSE: The extent of the hemodynamic and metabolic impairments in adult patients with moyamoya disease is still controversial. The aim of the present study was to evaluate the hemodynamic and metabolic status in relation to the development of basal moyamoya vessels (BMVs). METHODS: The cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2), oxygen extraction fraction (OEF), and cerebral blood volume (CBV) were measured using PET in ten patients with ischemic adult moyamoya disease (mean age, 36.6 years) and six age-matched normal controls (mean age, 33.3 years). The cerebrovascular reserve (CVR) after acetazolamide (ACZ) loading was also estimated using iodine-123 N-isopropyl-p-iodo amphetamine single photon emission computed tomography (123I-IMP SPECT). RESULTS: Based on the angiographic findings, eleven cerebral hemispheres with well-developed BMV (extensive BMV hemispheres) and nine cerebral hemispheres with diminished BMV (diminished BMV hemispheres) were identified. The main routes of collateral circulation in extensive BMV hemispheres were BMVs and leptomeningeal anastomoses. On the other hand, in diminished BMV hemispheres, transdural anastomosis was predominant, and leptomeningeal anastomoses were less developed. In cortices distal to the occluded internal carotid artery, the extensive BMV hemispheres exhibited a significantly lower CBF, CMRO2, CBF/CBV, and CVR (p < 0.05) and a significantly higher CBV and OEF than in diminished BMV hemispheres and controls (p < 0.05). Except for the CBF in the white matter, the mean hemodynamic and metabolic parameters of the diminished BMV hemispheres were not significantly different from those of the controls. CONCLUSION: The extensive development of basal moyamoya vessels is a sign of severe hemodynamic impairment in adult patients with ischemic moyamoya disease. The results may not apply to adults with hemorrhagic onset.

Adult↗
PubMed2003

Dielectric response in dilute lyotropic lamellar and sponge phases of a nonionic surfactant.

We study the dielectric response in lyotropic lamellar and sponge phases made up of a binary mixture of a nonionic surfactant and water. A single relaxation is observed in both phases within the measured frequency range of 10-10(7) Hz. This relaxation originates from the obstruction of electric current by insulating membranes. In the sponge phase, it depends on surfactant concentration and conductivity of solvent. The observed dependence is well-described quantitatively by the equivalent electric circuit of the sponge structure, including the effect of accumulation of ions at the interface between water and membrane. In the lamellar phase, there is little dependence of dielectric relaxation on surfactant concentration. This is presumably due to the fact that submicrometer-sized defects play a more important role in the electrical property in this phase than the lamellar structure in smaller length scales does. Our results offer some basic information to study more complicated systems composed of charged membranes in aqueous solution.

Journal Article↗
PubMed2003

Cerebral and cerebellar activation in power and precision grip movements: an H2 15O positron emission tomography study.

SUMMARY: Most human manual grip movements can be divided into power gripping and precision gripping, but central neural control during these tasks remains unclear. We investigated activation of the whole brain to analyze how simple hand movements are performed. The cerebral blood flow of seven healthy right-handed volunteers was measured by H2 15O positron emission tomography during right grip tasks without gripping a target object. Auditory-cued, repetitive power grips (i.e., fist making) and repetitive precision grips (i.e., opposition of the tip of the index finger and the tip of the thumb) were performed at 1.26 Hz. The areas activated during both tasks were the left primary sensorimotor cortex, caudal portion of the dorsal premotor, caudal portion of the supplementary motor area, cingulate motor area, and the right spinocerebellum and intermediate region of the cerebrocerebellum in comparison with the rest state. The analysis of power grip-precision grip tasks showed the activated peaks in the upper portion of the left sensorimotor area and right cerebellar vermis, but these areas were activated in both the tasks [(power grip-rest) and (precision grip-rest)] with uncorrected P < 0.001 as the statistical criterion. With P < 0.05 corrected as the statistical criterion, the results showed no significant activated peaks in regional cerebral blood flow. Our findings indicate no difference in brain activation between the acts of power grip and precision grip without a target object.

Adult↗
PubMed2003

Ipsilateral hemiplegia in a lateral medullary infarct--Opalski's syndrome.

A 42-year-old man was admitted complaining of the sudden onset of headache, vomiting, vertigo, and gait disturbance. The authors found hemiparesis of his right limbs, right Homer's syndrome, and decreased pain and temperature sensation of his right face and left limbs. Diffusion-weighted imaging (DWI) showed an acute small infarct located on the right side of the lateral lower medulla. This is the first report of Opalski's syndrome with lower medullary infarction detected by DWI.

Adult↗
PubMed2003

Heterogeneity of cerebral blood flow in Alzheimer disease and vascular dementia.

BACKGROUND AND PURPOSE: Alzheimer disease (AD) and vascular dementia (VaD) are the two major diseases that cause dementia, and early diagnosis is important. Single photon emission CT (SPECT) of cerebral blood flow (CBF) is used for the early detection of dementia and as an auxiliary method for follow-up. AD shows reduced posterior blood flow and VaD manifests reduced anterior blood flow on CBF SPECT images. We examined the usefulness of 3D fractal analysis of CBF SPECT images to objectively quantify the heterogeneity of CBF in patients with AD and VaD. METHODS: Thirty-two patients with AD and 22 with VaD based on neuropsychologic tests and imaging findings, as well as 20 age-matched control subjects underwent technetium-99m hexamethyl propyleneamine oxime CBF SPECT. We then conducted statistical image processing by 3D fractal analysis on reconstructed data. Fractal dimension, an index of heterogeneity, was then calculated for the whole brain, as well as for the anterior and posterior regions of the brain. A higher fractal dimension indicates that the CBF SPECT image is uneven. The ratio of fractal dimension of the anterior region to fractal dimension of the posterior region (A/P ratio) was calculated. Heterogeneity of CBF was compared among the AD, VaD, and control groups. RESULTS: Fractal dimensions of the AD, VaD, and control groups were 1.072+/-0.179 (mean +/- SD), 1.005+/-0.156, and 0.806+/-0.06, respectively. A significant difference of fractal dimension was noted between the control group and the two types of dementia (P<.0001); however, no significant difference was noted between the AD and VaD groups. The A/P ratios of the AD and VaD groups were significantly different (0.952 and 1.163, respectively; P<.01). CONCLUSION: Analysis of CBF SPECT images quantitatively showed that the fractal dimension was significantly higher (indicating heterogeneity) in patients with AD and VaD when compared with age-matched control subjects. Comparison of the A/P ratio on CBF SPECT images between AD and VaD groups showed that the heterogeneity of CBF was posterior-dominant for AD and anterior-dominant for VaD. Thus, 3D fractal analysis enabled a simple and objective evaluation of the heterogeneity of CBF in patients with AD and VaD.

Aged↗